The rail industry has historically been plagued by the loosening and loss of rail spikes from wood cross ties, and has periodically undertaken a variety of efforts in response to this documented need for improvement of the spike/tie interface. Spike loss is caused by the lateral and vertical movement of a rail under load (relative to the cross tie, hereinafter referred to jointly as "lateral forces"), which movement creates a ratcheting effect on the rail spike and the tie. This ratcheting eventually results in loosening and, ultimately, dislodgement and loss of the spike and thus further loss of stability of the rail at the tie. Frequent replacement efforts are undertaken to replace lost spikes, the industry standard method involving the steps of driving a wooden plug into the aperture in the tie created by the previously driven and now lost spike, followed be driving of a new spike into the plugged aperture. This means of replacement proves to be at least as unstable and susceptible to spike ratcheting as was the original installation, and thus spike replacement efforts may reoccur several times over the useful life of the tie.
Wood railroad cross ties are treated (typically with creosote) when manufactured to prevent erosion and wood rot. A properly treated tie has a useful life of approximately 25 years depending upon geographical location of tie installation. However, once a spike is driven into a tie, the area that is displaced by the spike becomes exposed to the elements, particularly as the lateral forces described above enlarge the area of displacement. This untreated exposed area around the spike thus captures moisture and microorganisms and is susceptible to freeze and thaw cycles which over time lead to degradation of wood fiber and internal rot around the spike, further weakening the hold between the tie and spike. Industry standard spike replacement methods do little or nothing to address this loss of tie integrity.
This degradation of the tie at and around the site of spike setting in the cross tie also shortens the useful life of the tie leading to premature replacement. Weakened rail ties are hazardous and therefore must be constantly inspected for and attended to. Spike and rail cross tie maintenance and replacement are, therefore, expensive and ongoing undertakings.
Various mechanical means of improving rail spike retention have heretofore been suggested and or utilized (see U.S. Pat. Nos. 2,777,641, 3,865,307, 3,519,205, 3,964,679, 4,203,193, and 5,758,821). Aside from the added expense of such mechanical solutions, many have done little to address the issue of tie degradation around a spike, and have thus met with limited success.
A number of compounds have been heretofore known and/or utilized for improving the strength of an anchor/situs interface (see U.S. Pat. Nos. 4,706,806, 4,723,389, 4,907,917 and 5,397,202). Many of these, however, are not readily adaptable to wood rail cross ties, involve two stage applications and/or require the external application of heat for mixing the compound and thus special tools on site.
Moreover, some such compounds by their nature are harmful to the environment and are thus not used for such wide spread applications as is necessary for railway roadbed maintenance. Some such compounds have also not achieved the longevity of securement of the anchor that is desired and/or have done little to address degradation in and around a spike when set in a wood tie.
In particular, it has been heretofore suggested that a mixture of asphalt and sand be used to improve spike-set life. This combination alone has not proved to be an adequate solution for the problem of improving spike retention and has not found acceptance. Further improvement in this vein could, however, be justified, since affordability and ease of application in the field are potentially achieved by such an approach.